Particular embodiments generally relate to systems and methods for efficient and reliable electronic communication using non-crystal reference oscillators.
Unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
Electronic communication devices and systems can transmit and receive frequency-modulated signals using designated bands of the electromagnetic spectrum. To organize and manage the limited bandwidth in the spectrum, various government and non-government organizations around the world regulate the usage of the locally available spectra to avoid interference between signals being transmitted within various bands of the spectrum.
For example, in the United States, the Federal Communications Commission (FCC) has segmented the electro-magnetic spectrum into bands of frequency ranges for designated uses. FIG. 1 shows a section of the spectrum and a few of the designated usage bands. Television stations are regulated to transmit in channels typically located in the 400 MHz to 800 MHz frequency range, cellular mobile communication operators and users are regulated to use the frequencies in the range from approximately 800 MHz to 2000 MHz, while devices for local and near field networking, such as IEEE 802.11 protocols, commonly known as “WiFi,” and Bluetooth operate in the 2.1 GHz to 5 GHz frequency range. Each of the ranges can be further separated into channels, i.e. smaller frequency ranges within the larger frequency ranges, centered on separated central frequencies that can be assigned to different users or entities or used by transmitting and receiving devices to send and receive signals without interfering with one another.
Since spectral bandwidth is a finite resource, regulating entities lease specific frequency bands subject to various rules and regulations to avoid unwanted interference between the leased bands. For example, such rules and regulations can require that any transmitter, using a particular leased frequency band or channel, transmits so that any signal intended to be transmitted and received on a specific channel remain within the designated frequency band. Similarly, users or devices transmitting in a particular frequency band, in order to efficiently and effectively use their designated or leased frequency band, try to reduce inter-channel interference by accurately transmitting and receiving signals at specific channels centered around a specific frequency.
FIG. 2 illustrates a conventional transmission system that is typically used to limit or prevent inter-channel interference. As shown in FIG. 2, an incoming bit stream 201 is received by transmitter Tx 203 and converted into a frequency-modulated signal 204 center around 0 Hz to be transmitted over various wired and wireless electronic communication media. A multiplier 205 converts the base frequency-modulated signal 204 into a frequency-modulated signal centered on a central frequency of a particular channel. Multiplier 205 changes the base frequency-modulated signal 204 by a multiple of a reference frequency. The reference frequency is provided by an external reference oscillator 207.
Oscillators, such as external reference oscillator 207, are often based on highly stable and reliable crystal-based oscillators or resonators, such as quartz-based electrical oscillators. Such crystal-based oscillators have proven to be highly reliable sinusoid signal generators that can be referenced for the up-conversion or detection of signals at specific frequency channels. In the example shown in FIG. 2, multiplier 205 references the regular signal output by external crystal-based reference oscillator 207 to convert the base frequency-modulated signal 204 into the up converted frequency-modulated signal 209 center around 2.4 GHz.
While such crystal-based signal transmitters have been widely adopted as the standard mechanism for transmitting electronic communication signals, crystal-based signal transmitters are generally expensive and contribute to the increased size and complexity of electronic communication devices. As electronic communication becomes more prevalent in all walks of life, ranging from personal and commercial communication, such as voice and data networks, to global positioning systems, and wireless broadcasting, like FM radio and TV signals, economic and technical requirements to reduce the size, complexity, costs, and power consumption of transmitting and receiving devices alike, continue to increase.
To reduce the size, complexity, cost, and power consumption of electronic communication devices, external crystal-based reference oscillators can be replaced with on-board non-crystal-based reference oscillators, such as CMOS-based electrical oscillators. However, conventional non-crystal-based reference oscillators generally are not as stable and, consequently, not as accurate as crystal-based reference oscillators. Non-crystal-based reference oscillators typically suffer from frequency variations based on operating conditions, such as temperature and driving voltage, and therefore, using such oscillators in electronic communication systems and devices presents a number of drawbacks and deficiencies relative to the use of crystal-based reference oscillators.